1. Field of Invention
The present invention relates to a lightning protection system for a construction, a method of creating a lightning protection system and use thereof.
2. Description of Related Art
A number of different lightning protection systems for protection of constructions are known within the art and have been known for several centuries. In particular, a type of construction which needs to be protected is wind turbines and their blades. Wind turbines are usually erected in open spaces or in the recent years at sea where they form the highest point and often attract lightning. The blades of the wind turbine reach the highest position and are therefore the usual place of impact for lightning.
In the past, the fact that blades were often made of a non-conductive material such as glass fibre lead to the belief that lightning was not a problem. However, such blades are often covered by a thin layer of dust, salt or pollution and together with moisture, the risk of conducting a current is real and results in several unprotected blades being damaged or destroyed by lightning.
The issue of establishing lightning protection for wind turbine blades has generated several different solutions.
A first solution is the use of a tape comprising a conductive layer with the tape being connected to a ground plane. The tape is positioned on the surface at the front edge of the blade from the tip of the blade and downwards. When lightning strikes the blade, the impact will usually be on the tape due to the path to the ground plane.
An example of this state-of-the-art is disclosed in EP-A 1011 182.
The surface-mounted tape generates a number of problems, such as inductive problems, which has lead to the development of lightning protection being built into the blade. The protection involves a metal wire with a ground plane connection which extends through the blade longitudinally and penetrates the surface close to the tip of the blade. The point of penetration attracts lightning which is then conducted to ground without damaging the blade.
The internal lightning protection has proved to offer reliable protection for blades of a limited length in the nearness of the point of penetration. With the development of ever longer blades, the system cannot protect the blade in its entire length. Especially, the internal system described above cannot protect a long blade with efficiency.
An example of this state-of-the-art is disclosed in WO-A 9607825.